This invention relates to tapered block copolymers of conjugated dienes and monovinylarenes.
In another aspect, this invention relates to a method of preparing tapered block copolymers of conjugated dienes and monovinylarenes.
Polymerization of styrene and butadiene with organolithium initiators to produce block copolymers in which one or more non-elastomeric polymer blocks are bonded to one or more elastomeric polymer blocks has been disclosed. Similarly, styrene and butadiene with terminal tapered blocks have been prepared by sequential charging of initiator and monomers to the polymerization zone to produce block copolymers suitable for manufacture of transparent colorless blister packages.
There is a continuing need for transparent colorless material suitable for shrink wrap packaging applications. Having better shrinkage properties exhibited at lower temperatures would facilitate the use of block copolymer shrink wrap in packaging applications.
There has also developed in the polymer field, and especially in the packaging and related industries, a need for thermoplastic polymers that can be formed into transparent articles having high impact strength with good environmental stress crack resistance. These should be suitable for use with conventional injection and blow molding equipment and also suitable for use in other methods of forming plastics into containers, tubes, films, fibers and the like. Polystyrene, high impact polystyrene, branched block copolymers, and the like have been developed to meet these criteria with various degrees of satisfaction. there is a continuing need for colorless transparent materials with high impact strength and good environmental stress crack resistance.